The present invention relates to melt blowing processes for producing non-woven mats. More specifically, the present invention relates to an apparatus and method for producing non-woven mats which form a sandwich of non-woven material having an intermediate layer of material different than the non-woven material.
In general, melt blowing processes are those in which a thermoplastic resin is extruded in molten form through orifices of heated nozzles into a stream of hot gas to attenuate the molten resin gas fibers, the fibers being collected on a receiver in the path of the fiber stream to form a non-woven or spun bonded mat. Various melt blowing processes have been described before, including those shown in the Buntin et al U.S. Pat. No. 3,849,241 and the Schwarz U.S. Pat. No. 4,380,570. In addition to these two patents, other efforts are described in other patents and publication, many of which are referred to in the Buntin et al patent.
Basically, the processes fall into two general classes, one of which is shown in the Buntin et al patent and the other in the Schwarz patent. In the Buntin patent, the stream of hot gas passes through elongated slots which are located on either side of a row of nozzles and with the elongated slots providing the stream of hot gas for all of the nozzles. In the Schwarz et al patent, each nozzle is individually surrounded by openings to provide for an individual stream of gas for each nozzle. The present invention, however, can operate with either of the systems, but it is preferred that the invention operate with the type of system shown in the Schwarz patent as will become apparent with a further description of the present invention.
The non-woven mats produced by the melt blowing processes described above have been used to provide for many different applications. One such application is filtering of various types. Specifically, the non-woven mats may be formed into flat filters which can be used to filter either gases or liquids. Also, the non-woven mats may be formed into various shapes such as filter masks used to provide for individual filtering by the user of the face mask. In any event, it is often desired to improve the characteristics of the non-woven mat such as the filtering capability by either using additional layers of the non-woven mat or by incorporating additional material different than the non-woven mat. One example would be the use of activated charcoal within the filter structure.
In the past, activated charcoal may be placed between two separate layers of non-woven material and with the edges sealed to capture the charcoal material within the layers of non-woven material. In order to provide for such a structure, the individual mats of non-woven material must be produced separately and with a completely separate operation provided in which one layer is positioned to receive a layer of activated charcoal and then a second layer of non-woven material placed over the layer of activated charcoal to provide for the sandwich structure of the two layers of non-woven material capturing the activated charcoal. It would be appreciated that such a method is cumbersome and is expensive.